Apparatus and method for mold charging



v. E. VALENTINE ErAL 2,959,816

APPARATUS AND METHOD FOR MOLD CHARGING 2 Sheets-Sheet 1 Nov. 15, 1960 Filed June 11, 1957 INVENTORS FIG, 2 VAUGHN EVALENTINE a MATTHEW .1. z KER ATTORNEYS Filed June 11', 1957 r v. E. VALENTINE EI'AL APPARATUS AND METHOD FOR MOLD CHARGING 2 Sheets-Sheet'Z 25 44 2s 42 53 I4 54 I2 42 FIG. 4

INVENTORS VAUGHN E. .ALENTINE a BNXAIATTHEW J. ZOKER ATTORNEYS United States Patent AND METHOD FOR MOLD CHARGING Filed June 11, 1957, Ser. No. 665,016

9 Claims. 01. 18-26) APPARATUS The present invention relates to improvements in the charging of molds for rotational casting. More particularly, the invention embodies a concept whereby a viscous fluid charge of casting material is enclosed within a thin casing or integument which is sealed to form a pliable or distensible bag. The sealed bag with the casting material encased therein is then placed within a mold component of special construction, mechanical pressure is applied to stretch and rupture the bag, and the fluid casting material is discharged into the mold interior. The new empty bag cooperates with the mold cap to form a seal, so that the casting material will not be thrown out of the mold during the casting operation.

In the production of objects by rotational casting technique a hollow mold is used. When the casting material has been introduced into the interior thereof, the mold is closed and locked and subjected to simultaneous rotation upon different, and preferably divergent, axes which will distribute the casting material evenly over the inner surface of the mold. During rotation, the mold is carried through a heating oven which gels and sets the casting material which has been distributed over the inner mold surface. After the casting material is set, rotation of the mold is stopped, the mold is cooled to a degree such that it can be opened, and the finished object is removed; whereupon the mold is readied for repeating the cycle. 1

Suitable rotational casting apparatus for the practice of the invention is disclosed in the US. patent to Martin and Rekettye, No. 2,629,131, issued February 24, 1953. For a disclosure of rotational casting technique, see the US. patent to Molitor, No. 2,629,134 also issued February 24, 1953.

Heretofore, the casting material has been mixed in large batches, stored in a tank, and fed by suitable conduits to a pump for delivering a measured charge of the material to each mold. Various nozzles have been em ployed for delivering the measured charge of material from the pump to the mold interior. The casting material, when delivered to the mold, is quite viscous and stringy and so tends to cling to the mouth of the nozzle and drip upon the mold exterior and the casting apparatus. Recently, nozzles of improved design have been perfected which significantly minimize the problem of dripping. However, such nozzles are better adapted for the filling of larger molds, requiring for example a fluid charge of 100 grams or more, and have certain objections when used for the charging of molds requiring small and very accurately measured amounts of casting material.

Therefore, it is an object of the present invention to provide improved method and apparatus for the charging of molds with a viscous fluid casting material.

Further, it is an object to provide for the charging of molds adapted for rotational casting with a very accurately measured amount of casting material.

Still further, it is an object to provide for the charging of rotational casting molds in such a manner as will substantially eliminate waste of casting material, which will ensure accuracy and uniformity when a quantity of identical objects are being produced, and which will expedite the charging of a mold so that it can be quickly returned to the molding cycle.

These and other objects of the inventionwill be apparent from the following description of the invention and the attached drawings.

In the drawings:

Fig. 1 is a view, partly in elevation and partly in section, of a sealed bag with a charge of casting material therein;

Fig. 2 is an exploded view of a mold carrier suitable for use in the practice of the invention;

Fig. 3 is a fragmentary view of certain of the apparatus elements employed in the practice of the invention, prior to charging of the mold;

Fig. 4 is a view, similar to Fig. 3, showing the several apparatus elements subsequent to closing of a mold; and

Fig. 5 is a view, similar to Figs. 3 and 4, showing the several apparatus elements during the casting operation.

In a preferred form of the invention, the viscous fluid casting material may be a plastisol in the form of a polyvinyl chloride resin formulated with a suitable plasticizer, stabilizer, colorant and filler. By way of example, a suitable plastisol formulation includes: 100 parts of a P.V.C. resin; parts of a plasticizer such as DOP (dioctyl phthalate); 2 /2 parts of a stabilizer, such as a fatty acid salt of Ba, Cd, or Zn or mixtures thereof and l .5 parts of inert color pigment such as TiO The casing film should have sufficient strength so that the bag 12 with the charge 10 encased therein, can be handled by an operator. On the other hand, the film should be sufficiently thin (or weak) so that the bag 12 can be broken by the application of moderate mechanical pressure A polyvinyl film having a thickness of from one to three mils -will meet these requirements.

It will be understood that the techniques and apparatus employed for forming a sealed bag 12, with an accurately measured plastisol charge 10 therein, do not per se constitute a part of the invention. niques and apparatus are deemed to be within the purview of those skilled in the art. It is suggested that when the casing film 14 is of vinyl composition, a sealing apparatus employing induction heating means for softening the film is preferably employed. However, the use of induction heat scaling is exemplary only and other sealing, techniques such as cementing or stitching may also be used.

Referring to Fig. l, the bag 12 is preferablygenerally ing. Further, the air pocket 15 permits the, bag 12 to 1 assume the correct shape-and properly distend upon the Patented Nov.,15, 1960 Such techapplication ofmoderate pressure immediately prior to rupture thereof and the discharge of the charge into the mold interior. A sealed-bag 12 having an interior capacity at least 10 percent and not more than 25 percent greater than the volume of the chargedO'wvill generally sufiice for these purposes;

befilled with the charge 10, the remainder or minor amount being entrapped air;

Referring to Fig. 2, there is shown disassembled, a

mold carrier indicated generally by the numeral -20'and suitable for use in the practice of th'e invention; Such a type of mold carrier for rotational casting-isdisclosed in-a copending application of Paul Rekettye, filed February 16, 1956, and assigned Serial No. 566,036, and assigned to applicants assignee. Reference is made to'said rying a series of mold closures 25 for the molds 23; and

suitable locking means associated with the two assemblies for tightly closing the molds during a rotational casting process.

A mold carrier lower assembly 22 includes a bottom plate 28 having a fastening means such as a bolt 29for attachment to a casting apparatus (not shown). A mold carrying plate 30 is positioned above the bottom plate by a plurality of spacers 31. Each of the molds or mold bodies 23 depend through openings in the plate 30 and are provided with collar flanges 32 forming the open and upper portion of each mold. Around the upper surface of the mold carrying plate 30 are a series of stanchions 34, each rotatably supporting a clamping roller 35. Extending upwardly from thecenter of plate 30 is a splined shaft 38 which serves to center the lower assembly 22 with the upper assembly 24.

A mold carrier upper assembly 24 includes a plate 40 carrying the series of mold closures 25, one for each mold 23 on the lower assembly 22. Each closure 25 includes a lower or piston portion 42, described in further detail below, and a stem portion 43 extending through the plate 40. Seated between the plate 40 and the piston 42, around the stem 43, is a compression spring 44 which biases the piston 42 downwardly as described in further detail below. The upper plate 40 is provided with a series of slots (not shown) through which the stanchions 34 extend when the upper and lower assemblies are brought together by inserting the shaft 38 through a central bore 45 in the plate 40.

The upper assembly 24 further includes a locking plate 46, of smaller diameter than plate 40 and rotatable thereon, which carries on the periphery thereof a series of locking roller wedge plates 48. There is a wedge plate 48 for each stanchion 34 and suitable'means (not shown) may be provided for rotating the locking plate 46, so that the wedge plates 48 will engage the roller 35 on the stanchions and lock the upper and lower assemblies together.

It will be understood that the aforementioned elements, numerals 22 to 48, but excluding the piston 42, do not per se constitute a part of the invention and are deemed to be within the purview of the aforesaid application Serial No. 566,036.

When a mold 23 is charged according to the invention, the sealed bag 12 is positioned above the mold and moderate mechanical pressure is applied so that the bag will be stretched and ruptured to discharge the plastisol 10 into the mold interior. suitable for positioning the bag 12 is indicated generally bythe numeral 50.

As best shown in Fig. 3, the hollow moldextension In any event; the major amount" of the interioricapacity of "a bag "12 should:

A hollow mold componentmember 50 has a lower or funnel portion 51 adapted 'to be received and tightly seated in the mold collar flange 32. The interior wall of the. funnel 51 is downwardly tapered, in the manner of an inverted truncated cone, so that when a sealed bag 12 is placed within the member 50, the lower portion of the bag 12 will be shaped in the general form of an inverted cone. To facilitate rupture, the lower end or apex of the bag. 12 preferably extends, as indicated at 12a below the truncated end of the funnel 51.

Above the funnel 51 is the body or barrel portion 53 for the interior wall of barrel 53 is not critical so long as rupture of the upper portion of a bag 12 is avoided. Referring to Fig. 4, after a sealed bag 12 has been placed within a member 50 in the' manner shownin Fig. 3, the member is then seated the mold-collan flange 32. The lower assembly 22 and the upper assembly 24 of the mold carrier 20 is then assembled (see Fig.

2 and the description above) so that each mold closure 25is aligned with a mold member-50 atopeach mold-23. The lowerand upper assemblies of themoldcarrier-ZO are then locked together causing the mold closur'25 to enter the barrel 53 of the hollow member 50, contact the upper surface or base 12b ofthe sealedbag, and

distend the bag so that the lower end12a or-apex area will rupture.

A moderate pressure sufficient to gradually'distend and then ultimately rupture each bag 12 is supplied by the gradual compression of the mold closure springs 44 as the mold carrier 20 is assembled and locked. The configuration chosen for the moldclosure piston portion 42 is not critical so long as rupture of the upper portion of a bag 12 is avoided. It is preferred however, topr'ovide the piston 42 with a smaller diameter work area 42a so that the pressure will be applied to alimited area of the base 12b, axially aligned with the apex area 12a,

to ensure that the casing film 14 will rupture in the apex area. Another advantage of the smaller piston 'area 4211 is that the entrapped air 15 will be radially or laterally displaced to form a ring 15a aboutarea 42a and further ensure that the applied pressurewill be directed against;

.the apex area 12a of the bag.

Following complete assembly and locking of themold carrier 20 and rupture of the bag 12 so-as to discharge the plastisol 10 into the interior of the molds 23, the molds are ready for the casting process. While being subjected to the casting forces, the nowempty bag 12 will collapse in somewhat the manner shown in Fig. 5. Collapse of the bag 12 acts to seal the opening of the funnel portion'51.

As the casting operationcontinues including the applica portion 51 and will tend to tear free ofthe layer P when' the component 50 is removed. Any portion of the bag 12 which remains adhered to the layer P can be readily removed, as though it were fiash,.after the cast object has been stripped from the mold 23.

While a preferred embodiment of the invention has been shown and described, it will be apparent that changes and modifications could be made in the practice thereof without departing from the concept 0f the invention.

With regard to the formulation of the plastisol chargecld nd composition of the casing film- 14, the materials indicated above are exemplary only. Other and equivalent materials may suggest themselves to those skilled in the art. Accordingly, such modifications, changes and equivalent materials are intended to be within the scope of the subjoined claims.

What is claimed is:

1. A mold carrier for use with rotational casting apparatus comprising, a lower plate assembly carrying a plurality of open mold bodies and attachable to said apparatus, a plurality of mold extension members each having an open top, an open lower end insertable in a mold body and interior walls for supporting a sealed bag having distensible walls and containing a charge of fluid casting material, an upper plate carrying a plurality of mold closures insertable into the interiors of the mold extension members, and means associated with said lower assembly and upper plate for causing a mold closure to contact a sealed bag within each mold extension member and to apply pressure only suflicient to rupture the walls thereof so as to discharge said casting material into a mold.

2. A mold carrier according to claim 1 in which the interior walls of a mold extension member are generally in the shape of an inverted truncated cone.

3. In a mold carrier for use with rotational casting apparatus, said carrier including an open mold body, the combination with said mold body of: a mold extension member having an open top, an open lower end inserted in said mold body and interior walls for supporting a sealed bag having distensible walls and containing a charge of fluid casting material; a piston member insertable through the open top of said mold extension member; and means for applying pressure to said piston when inserted in said mold extension member only sufiicient to rupture the walls of said bag discharging the casting material into the mold interior.

4. In a mold carrier for use with rotational casting apparatus, said carrier including an open mold body, the combination with said mold body of: a mold extension member having an open top, an open lower end inserted in said mold body and interior walls defining generally the shape of an inverted truncated cone; a piston member insertable through the open top of said mold extension member; and means for applying pressure to said piston when inserted in said mold extension member only sufficient to rupture the apex area of a sealed bag located within said mold extension member below said piston member, said sealed bag having distensible walls and containing a charge of fluid casting material.

5. A method of introducting fluid casting material into the interior of an open mold, comprising the steps of: encasing a measured amount of said fluid material within a distensible fihn; confining said casing within said mold adjacent the mold opening substantially as an inverted cone with the apex thereof exposed; applying pressure to the base of said cone only suflicient to rupture the apex thereof; and, closing said mold with said film and fluid material therein.

6. A method of introducing fluid casting material into the interior of an open mold, comprising the steps of: encasing a measured amount of said fluid material within a distensible film; confining said casing within said mold adjacent the mold opening substantially as an inverted cone with the apex thereof exposed; applying pressure to the base of said cone in a limited area axially aligned with said apex only suflicient to cause said casing to rupture in the area of said apex; and, closing said mold with said film and fluid material therein.

7. A method of introducing fluid casting material into the interior of an open mold, comprising the steps of: forming a sealed casing of a distensible film so that a major amount of the capacity thereof is filled with said fluid material and the remainder of said capacity is entrapped air; confining said casing within said mold adjacent the mold opening substantially as an inverted cone with the apex thereof exposed; applying pressure to the base of said cone to displace said entrapped air radially thereof and only sufiicient to rupture the apex thereof; and, closing said mold with said film and fluid material therein.

8. A method of introducing fluid casting material into the interior of an open mold, comprising the steps of: forming a sealed casing of distensible film and enclosing therein a measured amount of said fluid material, the capacity of said casing when sealed being from 10 to 25 percent greater than the volume of said fluid material; confining said casing within said mold adjacent the mold opening substantially as an inverted cone with the apex thereof exposed; applying pressure to the base of said cone in a limited area axially aligned with said apex only sufficient to cause said casing to rupture in the area of said apex; and, closing said mold with said film and fluid material therein.

9. A method of introducing a polyvinyl chloride resin plastisol into the interior of an open mold, comprising the steps of: encasing a measured amount of said plastisol within a distensible polyvinyl film having a 1 to 3 mil thickness; confining said casing within said mold adjacent the mold opening substantially as an inverted cone with the apex thereof exposed; applying pressure to the base of said cone only sufficient to rupture the apex thereof; and, closing said mold with said film and plastisol therein.

References Cited in the file of this patent UNITED STATES PATENTS 1,977,580 Grier Oct. 16, 1934 2,042,917 Brandt June 2, 1936 2,287,277 Ryder June 23, 1942 2,327,079 Wacker Aug. 17, 1943 2,406,403 Rogers Aug. 27, 1946 2,624,072 Delacoste et a1 Jan. 6, 1953 OTHER REFERENCES Miller: Vinyl Products Can Make Your Future, from Rubber Age, February 1956; 2 pp. 

